This invention relates to a thin layer liquid film type evaporator, more particularly to a thin layer liquid film type evaporator used for separation and purification of mineral oils and solvents or condensation of substances which are not very susceptible to thermal cracking.
In the conventional apparatuses for separating and recovering a low boiling point component from a liquid mixture (feed), a combination of an evaporator and a condenser has frequently been employed. As the evaporator employed for such purposes, there is known a thin layer liquid film type evaporator, in which the feed is adapted to flow along the inner circumferential surface of a heating column in the form of a thin film so as to effectively evaporate the low boiling point component.
As a means for forming thin layer liquid film on the inner circumferential surface of the heating column in such thin layer liquid film evaporator, an impeller disposed at the upper central portion of the heating column so as to splash the feed against the inner circumferential surface of the heating column or a conical liquid film forming plate disposed at the uppermost position of the heating column so as to allow the feed to flow in the form of a film through the clearance formed between the outer edge of the film forming plate and the inner circumferential surface of the heating column is frequently employed.
However, in the case of the former, the drive unit for driving the impeller and the drive shaft of the impeller must be sealed, so that the constitution of the apparatus is complicated, leading unavoidably to rise in the production cost, and that maintenance of the rotary drive section becomes necessary.
Meanwhile, in the case of the latter, although the evaporator can be manufactured at a low cost because of its simple structure, it involves a problem that it is difficult to form appropriately a liquid film over the entire inner circumferential surface of the heating column but form a discontinuous film containing dry portions, lowering evaporation efficiency and causing coking of the heavy ends at the interfaces of the wet portions and dry portions.